Enforcing video output without monitor detection

fse · 10-09-2014, 08:53 PM

I tried to use a 27' iMac (Late 2009) as external monitor for a Windows 7 laptop using a Fujitsu Port Replicator (PR08). iMac supports a Mini-Displayport input with max. 2560x1440 pixels (in "Target Display Mode"), while PR08 provides a Displayport output (also with 2560x1440 pixels). I connected both with a MDP to DP cable. According to specs, it should work - but it doesn't.
Neither does Displaylink driver (latest version 7.7) detect iMac as monitor nor does iMac switch into "Target Display Mode" (via CMD-F2 shortkey). It seems, that each side requires the other side to do the first step! iMac only switch into monitor mode, if it detects a valid video signal. Displaylink provides only a video signal, if it detects a monitor.
My question: Can Displaylink drivers be forced to provide a video signal, even if no monitor is detected? It seems, that original Windows graphic drivers would support this, if my laptop would have a Displayport output.

Thanks.

JamesH · 10-10-2014, 07:55 AM

Hi,

DL-1xx based devices don't require a monitor to be present, DL-3xxx & DL-5xxx do.

Thanks,
James

fse · 10-11-2014, 11:43 AM

Hi James,

thanks for your reply. Unfortunately, DL-1xx does not support the required monitor resolution. From technical point of view, DL-3xxx & DL-5xxx should be able to provide a signal without a previous monitor detection. It's just a matter of driver implementation. I hoped, that there is kind of hidden debug feature, in order to omit this limitation of the driver GUI.

To me this means, that I have to sell again my new DisplayLink hardware in order to buy a laptop with native DisplayPort output based on an Intel GPU. Because Intel/Windows drivers support manual graphics configuration. That's too bad.

10-09-2014, 08:53 PM	#1
fse Junior Member Join Date: Oct 2014 Posts: 2	Enforcing video output without monitor detection I tried to use a 27' iMac (Late 2009) as external monitor for a Windows 7 laptop using a Fujitsu Port Replicator (PR08). iMac supports a Mini-Displayport input with max. 2560x1440 pixels (in "Target Display Mode"), while PR08 provides a Displayport output (also with 2560x1440 pixels). I connected both with a MDP to DP cable. According to specs, it should work - but it doesn't. Neither does Displaylink driver (latest version 7.7) detect iMac as monitor nor does iMac switch into "Target Display Mode" (via CMD-F2 shortkey). It seems, that each side requires the other side to do the first step! iMac only switch into monitor mode, if it detects a valid video signal. Displaylink provides only a video signal, if it detects a monitor. My question: Can Displaylink drivers be forced to provide a video signal, even if no monitor is detected? It seems, that original Windows graphic drivers would support this, if my laptop would have a Displayport output. Thanks.

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10-10-2014, 07:55 AM	#2
JamesH Senior Member Join Date: Jan 2012 Posts: 1,523	Hi, DL-1xx based devices don't require a monitor to be present, DL-3xxx & DL-5xxx do. Thanks, James

10-11-2014, 11:43 AM	#3
fse Junior Member Join Date: Oct 2014 Posts: 2	Hi James, thanks for your reply. Unfortunately, DL-1xx does not support the required monitor resolution. From technical point of view, DL-3xxx & DL-5xxx should be able to provide a signal without a previous monitor detection. It's just a matter of driver implementation. I hoped, that there is kind of hidden debug feature, in order to omit this limitation of the driver GUI. To me this means, that I have to sell again my new DisplayLink hardware in order to buy a laptop with native DisplayPort output based on an Intel GPU. Because Intel/Windows drivers support manual graphics configuration. That's too bad.